Information obtained in geological surveys using sonic and/or seismic waves (relatively low frequency waves) needs to be interpreted.
A common way of doing this is to take a sample, such as a core sample, from the region where the geological survey was taken and to subject the sample to typical subsurface conditions, such as stresses and pore fluid pressures. The sample is then analysed using ultrasonic waves (relatively high frequency waves) and obtained results are corrected such that at least some information for low frequency conditions can be estimated. However, such corrections introduce many uncertainties.
Consequently, it is desirable to acquire low frequency data of samples directly. So far, such attempts have been limited by technical constraints. In one known arrangement for measuring at low frequency, the entire measurement apparatus with sample is positioned in a pressure vessel to simulate subsurface conditions and low frequency measurements of the sample are taken within the pressure vessel. One disadvantage of this device is the limited range of pressures at which it can operate. A further disadvantage arises from the resonance frequency of the measurement apparatus. The measurement apparatus needs to be relatively small in order to be accommodated in a suitable pressure chamber. Such relatively small apparatus have relatively high resonance frequency (for example in the 10-20 Hz range), which limits the frequency range at which measurements can be taken. Further, the resonance frequency of the measurement apparatus is different within the pressure cell and outside the pressure cell and it is not a trivial task to identify contribution of such resonances for correction of data. An additional practical disadvantage is that the sample can only be relatively small.
In the light of the above, there exists a need for technological advancement.